For some years filters have been constructed having an outer casing and an upper closure cover, which enclose an inner chamber having an inlet for the liquid to be filtered and an outlet for the filtered liquid, and a filter cartridge having a tubular filter medium positioned inside the inner chamber to separate the chamber into a first region communicating with the inlet and a second region communicating with the outlet.
The filter cartridge is secured to the upper cover by an upper disc joined to the upper end of the filter medium and which, when consumed and needing replacement, is separated from the cover and replaced with a new cartridge.
Said filters are currently appreciated because the entire filter does not have to be scrapped and destroyed, but merely the spent filter cartridge. Accessibility to the cartridge is also facilitated in that, as this is secured to the closure cover of the casing, on opening the cover the cartridge follows it to emerge from the liquid in which it is immersed without having to be gripped with tools and without having to be shaken out or disengaged, which could cause damaging dirt to separate from it.
To secure the cartridge to the cover it is known (see U.S. Pat. No. 5,695,633 in particular) to use first coupling elements and second coupling elements which act together to achieve a mutual snap connection, the first coupling elements (or the second coupling elements) being joined to the cover and projecting axially towards the chamber interior and, vice versa, the second coupling elements (or the first coupling elements) being joined to the upper disc and projecting axially towards the upper cover.
A drawback of these filters is that, while there are no difficulties in coupling the cover and filter cartridge together, a considerable axial force is however required to separate these elements when a spent cartridge has to be replaced with a new one. If carried out manually, this separation operation, in addition requiring considerable force, can also, because of the fact that the spent cartridge is impregnated with oily impurities and miscellaneous dirt, cause these impurities and dirt to spatter all around, with the risk of soiling the operator and also the inner chamber of the filter.
An object of this invention is therefore to provide a filter of the aforedescribed type, in which the filter cartridge can be rapidly coupled to the casing cover and be easily and delicately released therefrom.